A centrifugal pump assembly is known from DE 101 15 989 A1, with which a rotor shaft is axially displaceable together with the impeller, so that the impeller can be moved into a position, in which its peripheral exit openings are closed. In this manner, the pump assembly can assume a valve function and block a flow passage.
Moreover, a pump assembly with two impellers which are driven via a common shaft is known from DE 30 02 210 A1. By way of axial movement of the shaft, these impellers can be displaced in the axial direction in each case between two exit channels, so that the impellers either deliver water from a primary circuit into a secondary circuit and back, or however only separately in the primary circuit and in the secondary circuit, depending on the axial position of the shaft. Thereby, a displacement device which is to be actuated hydraulically or pneumatically and which is arranged outside the pump assembly is provided for axial displacement of the shaft. Such a displacement device has the disadvantage that the shaft must be led out of the inside of the pump housing, so that a sealed feed-through must be provided.